Neil and Bill have it right: you can't tell by looking, and some combination of mechanical cleaning and ultrasonic cleaning is needed for older records. Maybe if one only bought new records an U/S machine alone would suffice, but I can't see why anyone would limit themselves to only new LPs!
Having said that, any cleaning is better than none, and even a simple vacuum machine will give you most of the auditory gains. When you see the minutiae of cleaning solutions, kHz and KW discussed, we are in the territory of diminishing returns. Those smaller gains may be very important to some, but you can have 80-90% of cleaning benefits just by doing it at all, by whatever means.